GB2245962A - Apparatus for heating fluid - Google Patents

Abstract

Apparatus for heating fluids, particularly for producing smoke, comprises a flattened fluid conduit (2) is held against a heat sink or between a pair of plates (4) forming a heat sink. Preferably an expansion chamber (5, 22) is provided at one or both ends of the undulating conduit. A heater (20) heats the plates (4) and thence the conduit (2) and a pump (31) or other pressure source (32) forces fluid through the conduit. The flattened shape of the conduit makes good contact with the heat sink and the expansion chamber(s) aim to prevent "spitting" or high back pressure. <IMAGE>

Description

APPARATUS FOR THE HEATING OF FLUID This invention relates to an apparatus for the heating of fluids, particularly for the production of smoke or mist for use in testing ventilation systems and fumigation and as theatrical effects.

It is known that certain liquids or liquid/gas mixtures when heated sufficiently will produce a smoke or mist.

Apparatus for producing such smoke or mist, are generally referred to as "smoke generating machines".

So called "water-based" glycol smoke generating machines usually rely on a heating chamber through which the fluid is forced under pressure to produce smoke/mist. This chamber can be made of a variety of metals, although it is usually made of aluminium. In construction the chamber either comprises a housing into which is cast a metal tubing or separate galleries welded together to form a single unit.

A heating means is used to raise the chamber to the required temperature so that the fluid therein will produce smoke or mist.

Production of such heating chambers is however expensive and requires sufficient accuracy in the casting process.

In addition the metal used for the tubing is Important.

The most successful metal from which to make coiled tubing is mild steel. It is, however, not ideal for this particular purpose due to its low thermal conductivity.

There is also the possibility of rust developing due to the presence of water in the fluid. Stainless steel as an alternative does not conduct heat fast enough to produce a good dry smoke.

The tubing for this purpose is ideally made from copper.

This however has the disadvantage that it cannot be cast into aluminium or other metals as the copper becomes "plastic", the result of which is that the copper tubing either splits or collapses.

Cast heating chambers also haves a tendency to spit hot fluid from the outlet of the machine during heating of the fluid.

Copper tubing can be used in an alternatively designed heating chamber. Here a circular length of copper tubing is sandwiched between two aluminium plates. While this design of a heating chamber enables copper tubing to be used, the resulting smoke output is low because the small contact area between the plates and the tubing only allows for a limited rate of heat transfer. A specific length of the tubing is used in order to ensure that the fluid reaches the correct temperature as it passes through the tube. Additionally the flow rate must be reduced by means of a low pressure pump or a restrictive needle tube.

There is therefore a need for an improved smoke machine capable of producing a good smoke at a relatively high flow rate.

Accordingly the present invention provides an apparatus for the heating of fluid comprising a flat-sided tubular fluid conduit having an inlet for the fluid to be heated and an outlet for the heated fluid, the fluid conduit being in thermal contact, along the flat sides thereof, with at least one thermal store means and a heating means.

Preferably the flat-sided fluid conduit is in thermal contact between two thermal store means.

Preferably the flat sided fluid conduit is arranged in a snake-like fashion between the two thermal store means.

The present invention also provides an improvement for removing excess hot fluid from smoke or mist produced by a smoke generating machine comprising an expansion chamber having a fluid inlet and a fluid outlet interposed between the inlet and the outlet of the fluid conduit of a machine.

The present invention further provides a method for heating fluids comprising passing a smoke-generating fluid through an apparatus for heating fluids as described in the above four paragraphs, the apparatus having been pre-heated to a suitable temperature.

The use of a flat-sided conduit greatly increases the area of contact between the conduit and the thermal store means. This increases the rate of thermal transfer and allows for an increase in the throughput of fluid.

Additionally the amount by which the conduit is compressed may act to aid control of the fluid flow rate. This arrangement therefore enables a high pressure to be used due to the ability of the system to accommodate a high flow rate and results in a high output of smoke/mist.

The thermal store means generally comprises a block of a thermally conductive material such as aluminium of a shape suitable to heat fluid in the conduit thermally coupled therewith. One example is a cylinder through which the conduit passes or around which it is wound.

By placing the fluid conduit between two thermal store means the fluid conduit can be heated from both sides thus increasing the rate of heat transfer between the conduit and the thermal store means. When the thermal store means are planar the conduit can be arranged along and across the surfaces of the two thermal store means, in a snake-like fashion. This arrangement of the conduit produces close thermal coupling between the thermal store means and the fluid conduit.

In a particularly compact embodiment of the present invention the fluid conduit is closely folded in the snake-like fashion between the two thermal store means so that adjacent "coils" are touching.

In order to overcome the problem of excess hot fluid in the resultant smoke "spitting" from the smoke outlet an expansion chamber of increased internal dimensions may be fitted to the outlet of a smoke generating machine. This chamber collects the excess hot fluid to be retained until it boils off. The chamber may be separately attached to or integral with the conduit. If attached it must form an airtight seal with the conduit.

The fluid conduit and the expansion chamber may be formed of any material that can withstand the high temperatures required to vaporise the fluid. They do not necessarily have to be made of the same metal but preferably are and are preferably both made of copper. As the machine has to be able to cope with the various requirements of different liquids, fluid conduits with various dimensions, may be used. However the diameter of the expansion chamber must always be greater than that of the conduits. The dimensions used are to optimise the residence time for a given fluid at a particular temperature of the heating means.

The heating means may be of any suitable form, but preferably takes the form of an electrical heater embedded into the or each thermal store means.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic plan view through a smoke generating machine without its upper plate.

Figure 2 shows a section through Figure 1 along the line, II-II and including its upper plate.

Figure 3 is an exploded perspective view of the machine of Fig. 1, and Figure 4 shows part of a second embodiment of the machine of Fig. 1.

Referring to the drawings, the smoke generating machine 1 comprises a single pipe 2, two plates 4, an expansion chamber 5, a heating means 20 embedded in the plates and means 21 for controlling the fluid flow and the heating means. A variable expansion chamber 22 is coupled to the inlet of pipe 2.

The pipe 2 consists of a small bore copper tube typically 60 inches (152 cm) long which has been compressed in a direction perpendicular to its longitudinal axis along its length thereby reducing its diameter from 0.125 in (3.18 mm) to 0.095 in (2.41 mm). The pipe 2 has an inlet 7 and an outlet 8 and is arranged between the inlet 7 and outlet 8 in a snake-like fashion with the flattened sides 6 in touching contact with the inner surfaces 3 of the plates 4. The plates 4 consist of slabs of aluminium and act as a thermal store for the heating means embedded therein. The heating means comprises an electrical heater element and is connected to the plates 4 enabling sufficient heat to be produced and transferred to the plates 4 to vaporise fluid passing through the pipe 2.

As is shown in Figures 1 and 3 there is attached to the pipe outlet 8 an expansion chamber 5 for removing excess hot fluid from the resultant smoke or mist.

The expansion chamber 5 is made of copper and carries a first tube 14 between its inlet and the pipe outlet 8 and a second tube 16 between its outlet and the apparatus's smoke outlet 12. The first tube 14 has an attachment means (not shown) by which an airtight seal is made with the pipe 2. The expansion chamber 5 is welded to the tubes 14 and 16.

The expansion chamber 5 has a sideways diameter greater than those of the first and second tube 14 and 16 respectively, but the depth is the same so that the chamber can fit between the plates 4. The enlarged diameter of the chamber 5 enables the excess fluid to collect within the chamber 5 and to be retained until it boils off.

As there is generally only a small amount of excess fluid the chamber 5 does not have to have a very large capacity but the precise dimension required may be varied according to the smoke generating fluid used.

This expansion chamber 5 may be used with any smoke generating machine wherein the tubing is formed by a separate casting process and is attached as herein described or cast as an integral unit with the tubing.

The machine is operated in accordance with standard practice. The heater 20 is switched on to preheat the pipe 2 before the fluid enters the machine 1. When the required temperature is reached, the fluid is forced under pressure from the inlet 7 along the pipe 2 and to the outlet 8 collecting heat as it moves along from the plates 4. The flat sides enable a greater transfer of heat than otherwise could occur.

In the smoke generating machine 1 as illustrated in Figure 1 the pipe 2 is arranged in a snake-like fashion with the coils 9 being separate from each other. The pipe 2 with the coil can however be folded with the coils 9 close together, preferably in touching contact.

Alternatively in a second embodiment the pipe may be a flattened pipe formed from 28 mm round tubing flattened to 2.5 mm and about 47 mm wide as shown at 2' in Fig. 4.

The fluid or resultant smoke or mist will thus be moving in opposite directions for each successive journey across the plates 4.

As the resultant smoke reaches the outlet 8, it enters an expansion chamber 5 where any excess fluid in the smoke collects and is retained until it is boiled off and exits through the outlet 12.

Details of the machine of Fig. 1 are shown in Fig. 3. As already described pipe 2 is located between heat sink aluminium plates 4 these being 6 mm thick. Either side of plates 4 are 1 mm thick steel pressure plates 24 and 25. A further plate 26 acting as a support plate of 1.2 mm thick steel secures the heater 20 on top of plate 25.

Bolts 27 are inserted through plates 24, 4, 4, 25 and 26 to be secured by nuts 28. The steel plates are assembled "oily" to blue at temperature.

Variable expansion chamber 22 which acts to smooth out back pressure indicated by broken lines 30 is connected between inlet 7 of pipe 2 and a pump 31 which pumps up the smoke generating fluid at a rate of about 4 ccisec.

from a 5 litre reservoir 32. The pump and reservoir can be replaced by an aerosol container 33 shown in broken lines.

The variable expansion chamber 22 is formed as a cylinder with a sealed air chamber 34 in which a free piston 35 can move under the influence of a pressure of about 80 psi (550 kN/m2) at inlet 36 from the pump or aerosol container or back pressure at outlet 37. The piston can be a freely movable membrane. The effect of a sudden increase in system pressure to say 150-160 psi (1030-1100 kN/m2) will be to force the piston or membrane in a direction to equalise the pressure. This prevents back pressure from slowing the flow rate through pipe 2.

It should be noted that the compression of pipe 2 as shown in Fig. 2 produces a restriction of flow compared to an uncompressed round pipe. Heat transfer is improved over known constructions. A further improvement is to introduce a sugar/water mixture into the pipe during manufacture and then to submit this to a high level of heating to cause a carbon deposit on inner surfaces of the pipe. The deposit creates a film which reduces thermal conductivity at points of high, temperature. This smooths the temperature gradient and alleviates pressure bursts. Furthermore, it has been found that if the pipe 2 is formed for the first third of its length from the inlet of copper/nickel piping with the remaining 2/3 from copper, the poorer heat transfer of copper/nickel again ensures a gentler heat gradient within the pipe so as to avoid back pressure.

The expansion chamber 5 is designed to overcome the problem of "spitting" small amounts of hot fluid on heat up. This chamber catches the small amounts of fluid and allows it to be harmlessly boiled off. As far as is known this is a novel feature of the machine according to the invention.

In prior art machines when the heat store has settled at a uniform high temperature, the possibility of pressure induced malfunction exists. This results from an enclosed slug of fluid expanding suddenly and forcing earlier slugs of fluid through the system at such a velocity as to decrease heat absorption by the fluid so that unvaporised fluid will be emitted.

In lower plate 24 a first notch 38 carries a thermostat 39 connected to control unit 21 and a second notch 40 is provided to carry an excess heat heat fuse 41 comprising a zinc melting element, the fuse is electrically connected to control unit 21 so that on heat overload, power to heater 20 and pump 31 is cut off.

Claims (20)

1. An apparatus for the heating of fluid comprising a flat-sided tubular conduit having an inlet for fluid to be heated and an outlet for the heated fluid, the fluid conduit being in thermal contact, along the flat sides thereof, with at least one thermal store means and a heating means.

2. Apparatus as claimed in claim 1 wherein the fluid conduit is in thermal contact between two thermal store means.

3. Apparatus as claimed in claim 1 or 2 wherein the or each thermal store means is formed as a metal plate.

4. Apparatus as claimed in any one of claims l to 3 wherein the or each thermal store means is formed as an aluminium plate.

5. Apparatus as claimed in any one of claims 1 to 4 wherein the fluid conduit is formed in a snake-like fashion.

6. Apparatus as claimed in any one of claims 1 to 5 wherein the fluid conduit is formed as a continuous flattened pipe.

7. Apparatus as claimed in any one of claims 1 to 5 wherein the fluid conduit is formed as a plurality of flattened pipe sections interconnected by round pipe sections.

8. Apparatus as claimed in any one of claims 1 to 7 wherein the fluid conduit is formed along its length of one length at or towards the outlet of a first and high conductivity metal or alloy and of a second length of a second and lower conductivity metal or alloy at or towards the inlet.

9. Apparatus as claimed in claim 8 wherein substantially two thirds of the length of the conduit being said one length is formed from copper and the second length is formed from a copper/nickel alloy.

10. Apparatus as claimed in any one of claims 1 to 9 wherein an expansion chamber is connected to the conduits outlet for fluid communication therewith.

11. Apparatus as claimed in any one of claims 1 to 10 wherein an expansion chamber is connected to the conduits inlet for fluid communication therewith.

12. Apparatus as claimed in any one of claims 1 to 11 further comprising a pump in fluid communication with the conduits inlet.

13. Apparatus as claimed in any one of claims 1 to 11 further comprising an aerosol container connection in fluid communication with the conduit's inlet.

14. Apparatus as claimed in claim 11 wherein the expansion connected to the inlet comprises a piston or flexible membrane mounted in a chamber so as to smooth pressure fluctuations between an inlet and outlet of the chamber.

15. Apparatus as claimed in any one of claims 1 to 14 wherein the fluid conduit is sandwiched between two metal thermal store plates, the fluid conduit and store plates in turn sandwiched between pressure plates.

16. Apparatus as claimed in claim 5 wherein the heating means is mounted between one said pressure plate and a further plate.

17. Apparatus as claimed in any one of claims 1 to 16 further comprising a thermostatic control in thermal communication with the fluid conduit.

18. Apparatus as claimed in any one of claims 1 to 17 further comprising a heat fuse in thermal communication with the fluid conduit, the fuse being so connected with a control unit as to cut off power to the heating means.

19. Apparatus as claimed in any one of claims 1 to 18 wherein the fluid conduit is provided with a carbon deposit on inner surfaces thereof.

20. Apparatus for the heating of fluid substantially as described with reference to the accompanying drawings.